Water-in-oil polymer emulsion and method for making same

ABSTRACT

The invention concerns a water-in-oil polymer emulsion containing in an organic and continuous phase practically non-miscible in water, finely comminuted water soluble polymers or capable of being swollen in water, a water-in-oil emulsifying agent and optionally wetting agents. The invention also concerns a method for preparing said emulsion. More particularly, it concerns a method for invert emulsion in the presence of one or several initiators belonging a specific family of azacarboxylic acid esters.

The present invention relates to a water-in-oil polymer emulsioncontaining, in a continuous and virtually water-immiscible organicphase, finely divided water-swellable or water-soluble polymers, awater-in-oil emulsifier and optionally wetting agents. The inventionalso relates to a process for preparing said emulsion.

Water-in-oil polymer emulsions of water-soluble polymers are known.Processes for preparing them by reverse emulsion polymerization are alsoknown. Reference may be made to document U.S. Pat. No. 3,284,393, whichis the reference patent in this field.

The process as described in U.S. Pat. No. 3,284,393 consists ofemulsifying, in an organic phase, one or more water-solubleethylenically unsaturated monomer(s), optionally in aqueous solution,using a water-in-oil emulsifier, and then in performing emulsionpolymerization in the presence of an initiator. Benzoyl peroxide,lauroyl peroxide and potassium persulfate are mentioned as free-radicalinitiators. These peroxides have also been mentioned in U.S. Pat. No.3,920,599.

U.S. Pat. No. 4,059,552 describes finely divided water-swellablepolymers and mentions tert-butyl hydroperoxide, dimethane sulfonylperoxide and ammonium persulfates as polymerization initiators.

It is found, however, that, in the most recent processes,azobisisobutylronitrile is most commonly used (See U.S. Pat. Nos.4,024,097, 4,713,431, and 4,419,344) as a reverse emulsionpolymerization initiator.

Moreover, U.S. Pat. No. 5,292,800 discloses water-in-oil polymeremulsion, in which the organic phase consists of at least 50% plant oranimal oils. Comparative Example 1 of said patent shows that, bypolymerizing at 55° C., 250 g of an aqueous 50% solution of acrylamidein 250 g of rapeseed oil in the presence of dimethyl 2,2′-azobis(isobutyrate) as initiator and using a commercial sorbitan monooleate asan emulsifier, a granular and unfiltrable water-in-oil polymer emulsionis formed.

Applicants have now developed a process for preparing a stable reverseemulsion having an organic phase of less than 50% by weight. Inaddition, it makes it possible to reduce or even eliminate the problemsof formation of coagulates or of grains that are encountered during thepolymerization. This process also makes it possible to prepare polymerswith high molecular masses, this property being particularlyadvantageous for increasing their efficacy in applications such asflocculation, etc.

The process, according to the present invention, comprises emulsifying,in an organic phase, one or more ethylenically unsaturated monomer(s),using a water-in-oil emulsifier and then performing an emulsionpolymerization, wherein the polymerization is performed in the presenceof one or more initiator(s) belonging to the family of azocarboxylicacid esters, represented by formula (I).

in which:

R₁, R₂, R₃ and R₄, which may be identical or different, are selectedindependently from the group consisting of linear or branched-alkylscontaining from 1 to 9 carbon atoms are preferably from 1 to 4 carbonatoms, optionally substituted with one or more substituents selectedfrom hydroxyl, C₁ to C₆ alkoxy and halogen substituents; C₃ toC₁₂-cycloalkyls, optionally substituted with one or more substituentsselected from C₁ to C₆ alkyl, C₁ to C₆ alkoxy, hydroxyl and halo groups;

-aralkyls optionally substituted with one or more C₁ to C₆ alkyl, C₁ toC₆ alkoxy, hydroxyl and halo groups;

-aryls optionally substituted with one or more substituents selectedfrom C₁ to C₆ alkyl, C₁ to C₆ alkoxy, hydroxyl and halo groups;

with at least one of the combinations R₁-R₂ and R₃-R₄ possibly formingan aliphatic ring; R″ and R′ are identical to or different than eachother and are selected independently from the group consisting of linearor branched C₁ to C₁₀ and preferably C₁ to C₄ aliphatic radicals.

The advantage of these azocarboxylic acid esters is their low meltingpoint, which is generally less than 27° C. The preferred azocarboxylicacid esters are those in which R″ and R′ represent methyl or ethyl andin which R₁, R₂, R₃ and R₄ advantageously represent C₁ to C₄ alkylgroups.

The azocarboxylic acid ester that is particularly preferred is diethyl2,2′-azobisisobutyrate, that is to say with R₁, R₂, R₃ and R₄representing methyl and R′ and R″ representing ethyl. DEAB may also beused as a mixture with other azocarboxylic acid esters. Mention may bemade, for example, of mixtures of diethyl 2,2′-azobisisobutyrate (DEAB)and of dimethyl 2,2′-azobisisobutyrate (DMAB) with a mass content ofDEAB of greater than 50%, and mixtures of DEAB, DMAB and 2-methyl2′-ethyl azobisisobutyrate with a COOCH₃/COOC₂H₅ molar ratio ≦10.

The azocarboxylic acid esters of formula (I) may be prepared by astandard two-step process comprising a first step of converting theazonitrile, by reaction with an alcohol, in the presence of HCl,according to the Pinner reaction, leading to the corresponding azoiminoether hydrochloride, and a second step of hydrolysis in the presence ofthe hydrochloride thus obtained. They may also be prepared by theimproved processes as described in documents DE 2 254 575, EP 80 275 andEP 230 586.

In addition, these esters may be prepared by reacting an azonitrile withan alcohol and hydrochloric acid in an aromatic solvent, with anHCl/azonitrile molar ratio >2 when the alcohol is methanol and >3 whenthe alcohol is ethanol or a higher alcohol.

The amount of azocarboxylic acid esters used in the process according tothe present invention represents about 0.01 to 1% by weight of theethylenically unsaturated monomer(s) used and preferably 0.02% to 0.5%by weight.

The water-soluble ethylenically unsaturated monomers or the mixtures ofwater-soluble monomers, comprising water-soluble ethylenicallyunsaturated monomers and water-insoluble ethylenically unsaturatedmonomers, are preferred.

Water-soluble ethylenically unsaturated monomers that may especially bementioned include unsaturated monoethylenic carboxylic acids, forinstance acrylic acid, methacrylic acid, maleic acid, itaconic acid, andsalts of the abovementioned carboxylic acids, for example the sodium,potassium or ammonium salts, esters or acrylic acid and methacrylic acidand of amino alcohols such as, for example, dimethylaminoethyl acrylate,in protonated or quaternized form, for example dimethylaminoethylacrylate hydrochloride, dimethylaminoethyl acrylate hydrogen sulfate orbisulfate, dimethylaminoethyl acrylate methyl chloride,dimethylaminoethyl acrylate methyl sulfate, dimethylaminoethylmethacrylate hydrochloride, dimethylaminoethyl methacrylate hydrogensulfate or bisulfate, dimethylaminoethyl methacrylate methyl chloride,dimethylaminoethyl methacrylate methyl sulfate, acrylamide,methacrylamide, N-alkyl(meth)acrylamides,methacrylamidopropyltrimethylammonium chloride,acrylamidopropyltrimethylammonium chloride,methacrylamidopropyltrimethylammonium methyl sulfate,acrylamidopropyltrimethylammonium methyl sulfate, acrylamido- andmethacrylamidoalkylsulfonic acids and salts thereof, such as2-acrylamido-2-methylpropanesulfonic acid, hydroxyalkyl acrylates andhydroxyalkyl methacrylates, vinylsulfonic acid, vinylphosphonic acid,N-vinylamides such as, for example, N-vinyl-formamide, N-vinylacetamide,N-vinyl-N-methylacetamide and N-vinyl-N-methylformamide,diallyldimethylammonium chloride, N-vinylpyrrolidone, N-vinylimidazole,N-vinylimidazoline, 2-methyl-1-vinylimidazoline, 2-ethylsulfonicmethacrylic acid, styrenephosphonic acid and styrene sulfonic acid.Mention may also be made of N-methylolacryamide andN-methylolmethacrylamide, and also of N-methylol(meth)acrylamides whichare partially or totally etherified with monohydroxylated C₁ to C₄alcohols.

These monomers may be cationic or anionic and, in certain cases, theionic charges are small enough for the monomers to be considered asnonionic.

The cationic monomers are, for example, allylic amines or diallylicamines or dimethylaminoethyl methacrylate or quaternary salts such asethyltrimethylammonium acrylate chloride, ethyltrimethylammoniummethacrylate chloride, acrylamidopropyltrimethylammonium chloride anddiallyldimethylammonium chloride.

The anionic monomers are, for example, acrylic acid or methacrylic acid,2-(meth)acrylamido alkylsulfonic acid and salts thereof, vinylphosphonic acid, styrene sulfonic acid and styrene phosphonic acid.

The water-soluble mixture of monomers that is particularly suitable forthe invention consists of acrylamide and of at least one monomer chosenfrom ethyltrimethylammonium acrylate chloride, ethyltrimethylammoniummethacrylate chloride, acrylamidopropyltrimethylammonium chloride,diallyldimethylammonium chloride, acrylic acid and methacrylic acid.

The organic phase consists of an inert hydrophobic liquid and generallyrepresents between 10% and 49% of the total weight of the emulsion andpreferably between 20% and 40%.

The inert hydrophobic liquid may be chosen from a wide range of organicliquids comprising liquid hydrocarbons and substituted liquidhydrocarbons, preferably containing from 4 to 8 carbon atoms or evenmore than 8 carbon atoms. For example benzene, xylene, toluene, mineraloils, kerosene, heavy spirits and, in certain cases, petroleum can beused. Petroleum fractions and in particular in branched-chainisoparaffinic fraction sold under the brand name “Isopar M” have beenfound to be particularly advantageous.

The water-in-oil emulsifier that are suitable are those with an HLB(hydrophilic-lipophilic balance) value between 2 and 10 and preferablybetween 3 and 9. For the definition of the HLB value, reference may bemade to the article by W. C. Griffin in Journal of Society of CosmeticChemist, Volume 1, 311 (1950).

Examples that may be mentioned include fatty acid esters of mono-, di-and polyglycerols, for instance the monoleate, the dioleate, themonostearate, the distearate and the palmitostearate. These exters maybe prepared, for example, by esterifying mono-, di- and polyglycerols,or mixtures of polyhydroxylated alcohols such as ethylene glycol,diethylene glycol, dipropylene glycol, 1,4-butanediol,1,2,4-butanetriol, glycerol, trimethylolpropane, sorbitol, neopentylglycol and pentaerythritol.

In addition, mention may be made of fatty acid esters of sorbitan, forinstance sorbitan monoleate, sorbitan dioleate, sorbitan trioleate,sorbitan monostearate and sorbitan tristearate.

Fatty acid esters of mannitol, for instance mannitol monolaurate ormannitol monopalmitate, fatty acid esters of pentaerythritol, forinstance pentaerythritol monomyristate, pentaerythritol monopalmitateand pentaerythritol dipalmitate, fatty acid esters of polyethyleneglycol sorbitan, more particularly the monooleates, fatty acid esters ofpolyethylene glycol mannitol, more particularly the monooleates andtriolates, fatty acid esters of glucose, for instance glucose monooleateand glucose monostearate, trimethylolpropane distearate, the products ofreaction of isopropylamide with oleic acid, fatty acid esters ofglycerol sorbitan, ethoxylated alkylaines, sodium hexadecyl phthalateand sodium decyl phthalate may also be suitable as emulsifiers.

The polymerization temperature depends on the decomposition kinetics ofthe initiator used and is generally between 10 and 100° C. andpreferably between 30 and 90° C.

According to the process of the present invention, the process ispreferably performed in the absence of oxygen. A flow of inert gas suchas nitrogen or argon may be used to purge the installation. It has beenfound that, in the absence of oxygen in the reaction medium, thepolymers obtained are reproducible, the molar masses are higher and thecontent of residual monomer is lower.

The process of the present invention also has the advantage of notleading to the formation of toxic byproducts.

The polymers thus obtained may be used as flocculants in thepurification of urban and industrial waste water, in the paper industry,in mines, quarries and drilling muds, in the assisted recovery ofpetroleum, and in the treatment of drinking water.

EXPERIMENTAL SECTION

Isopar M: Paraffinic hydrocarbon from Exxon

Span 80: Sorbitan monooleate from ICI

Tween 61: Polyethoxylenated sorbitan monostearate (4 mol of PEO) fromICI

AZDN: 2,2′-azobisisobutyronitrile sold by Elf Atochem

DMAB: Dimethyl 2,2′-azobisisobutyrate

DEAB: Diethyl 2,2′-azobisisobutyrate

EDTA: Ethylene diaminetetraacetic acid.

The amount indicated in the general procedure corresponds to 100 gramsof monomers used.

General Procedure

Preparation of the aqueous phase:

The following products are successively introduced into a beaker withstirring:

demineralized water 176.35 g acrylamide (50% in water) 335.91 g AdamquatMC-80 50.00 g EDTA 0.08 g adipic acid 12.60 g NaOH (50% in water) 1.68 gNaCl 12.60 g

Preparation of the oil phase:

The following products are successively introduced into a 1 liter Wolffflask:

Isopar M 218.67 g Span 80 18.60 g Tween 61 2.20 g

Preparation of the monomer emulsion:

The aqueous phase prepared above is poured into the oil phase. The twophases are homogenized using an Ultra-Turrax blender for 2 minutes.

Polymerization reaction:

The monomer emulsion obtained above is poured into a polymerizationreactor equipped with a twin turbomixer set at 500 rpm, a condenser anda dipped tube fed with nitrogen. This emulsion is then maintained for 30minutes under a nitrogen sparge and is brought to 47° C. The azoinitiator (0.15 part) is then introduced while maintaining thetemperature of the reaction medium at 47° C.±2° C. for 2 hours 30minutes. A steady temperature of 52.5° C. is then maintained for 1 hour,followed by a second steady temperature of 80° C. also for 1 hour. Thereaction medium is then cooled to room temperature and transvased byfiltering the mixture the mixture through a 10 μm filter. The amount ofgrains possibly formed is measured after drying in an oven for 24 hoursat 40° C. The content of the grains is calculated by determining theratio of the amount of grain obtained and of the theoretical amount ofpolymer formed.

The intrinsic viscosity of the polymers isolated by precipitation of 10g of reverse emulsion in 100 g of acetone is measured. The polymer thenbeing taken up in 300 ml of acetone to give a powder which is dried for24 hours in an oven at 40° C.

0.5 g of copolymer is dissolved in 200 ml of an aqueous molar NaClsolution. This solution is rediluted several times and the correspondingkinematic viscosities are measured each time. The intrinsic viscositymay then be determined.

EXAMPLES 1 2 3 Initiator AZDN DMAB DEAB Grain content 3.7% 0% 0%Intrinsic viscosity (dg/l) 12.7 15 12.5

EXAMPLE 4

The reaction is performed as described above, but maintaining apolymerization steady temperature of 45° C. instead of 47° C. and usingDMAB as initiator.

EXAMPLE 5 Initiator DMAB Grain content 0% Intrinsic viscosity (dg/l) 17

What is claimed is:
 1. A process for preparing a water-in-oil polymeremulsion, said process comprising emulsifying, in an organic phase, atleast one ethylenically unsaturated monomer, using a water-in-oilemulsifier and performing an emulsion polymerization; wherein saidpolymerization is performed in the presence of at least one initiator offormula

wherein R₁, R₂, R₃ and R₄ each independently comprise: (i) linear orbranched-alkyl group containing from 1 to 9 carbon atoms, wherein said-alkyl group is optionally substituted with at least one hydroxyl group,C₁ to C₆ alkoxy group, halogen group, or a combination thereof; (ii) C₃to C₁₂-cycloalkyl group, wherein said -cycloalkyl group is optionallysubstituted with at least one C₁ to C₆ alkyl group, C₁ to C₆ alkoxygroup, hydroxyl group, halo group, or a combination thereof; (iii) an-aralkyl group, wherein said -aralkyl group is optionally substitutedwith at least one C₁ to C₆ alkyl group, C₁ to C₆ alkoxy group, hydroxylgroup, halo group, or a combination thereof; (iv) an -aryl group,wherein said -aryl group is optionally substituted with at least one C₁to C₆ alkyl group, C₁ to C₆ alkoxy group, hydroxyl group, halo group, ora combination thereof; wherein, optionally, at least one combination ofR₁-R₂ and/or R_(3-R) ₄ form an aliphatic ring; and wherein R″ and R′independently comprise linear or branched C₁ to C₁₀ aliphatic radicals.2. The process of claim 1, wherein said linear or branched alkyl groupcontains from 1 to 4 carbon atoms.
 3. The process of claim 1, whereinsaid R″ and R′ independently comprise linear or branched C₁ to C₄aliphatic radicals.
 4. The process of claim 1, wherein R″ and R′comprise methyl or ethyl groups and R₁, R₂, R₃ and R₄ comprise a C₁ toC₄ alkyl radical.
 5. The process of claim 4, wherein R″ and R comprisean ethyl radical and R₁, R₂, R₃ and R₄ comprise a methyl radical.
 6. Theprocess of claim 1, wherein at least one of said initiator is diethyl2,2′-azobisisobutyrate.
 7. The process of claim 6, wherein said processcomprises more than one initiator of formula (I) and at least one ofsaid initiator is diethyl 2,2′-azobisisobutyrate.
 8. The process ofclaim 1, wherein said process is performed in the absence of oxygen. 9.The process of claim 1, wherein said process comprises a polymerizationtemperature of between about 10° C. and about 100° C.
 10. The process ofclaim 9, wherein said polymerization temperature is between about 30° C.and about 90° C.
 11. The process of claim 1, wherein said organic phasecomprises an inert hydrophobic liquid.
 12. A water-in-oil polymeremulsion prepared by emulsifying, in an organic phase, at least oneethylenically unsaturated monomer, using a water-in-oil emulsifier andperforming an emulsion polymerization; wherein said polymerization isperformed in the presence of at least one initiator of formula

wherein R₁, R₂, R₃ and R₄ each independently comprise: (i) a linear orbranched-alkyl group containing from 1 to 9 carbon atoms, wherein said-alkyl group is optionally substituted with at least one hydroxyl group,C₁ to C₆ alkoxy group, halogen group, or a combination thereof; (ii) aC₃ to C₁₂-cycloalkyl group, wherein said -cycloalkyl group is optionallysubstituted with at least one C₁ to C₆ alkyl group, C₁ to C₆ alkoxygroup, hydroxyl group, halo group, or a combination thereof; (iii) an-aralkyl group, wherein said -aralkyl group is optionally substitutedwith at least one C₁ to C₆ alkyl group, C₁ to C₆ alkoxy group, hydroxylgroup, halo group, or a combination thereof; or (iv) an -aryl group,wherein said -aryl group is optionally substituted with at least one C₁to C₆ alkyl group, C₁ to C₆ alkoxy group, hydroxyl group, halo group, ora combination thereof; wherein, optionally, at least one combination ofR₁-R₂ and/or R₃-R₄ form an aliphatic ring; and wherein R″ and R′independently comprise linear or branched C₁ to C₁₀ aliphatic radicals.